The present invention generally concerns a device and a method for limiting exhaust particulate emission when supercharging internal combustion engines. More specifically, the present invention concerns a supercharged internal combustion engine provided with a pressure wave machine such as a turbocharger having a charge air flap valve and/or a recirculation flap valve and/or an exhaust gas by-pass valve, and exhaust gas conduits or elbows leading to an exhaust gas receiver.
Particulate emission from internal combustion engines has already been limited by law in some countries. Other countries will follow with more severe and restrictive implementation of regulations concerning the allowable limits for the emission of particulates in exhaust gases.
The particulate emission of internal combustion engines is essentially made up of the following components:
Suspended soot, PA0 Hydrocarbon compounds and other organic substances adhering to the soot, PA0 Sulfate compounds, and PA0 Lead compounds (in the case of spark-ignition engines)
Reduction of the particulate emission from internal combustion engines by measures taken inside the internal combustion engine is not yet possible given the present state of the art, but advances have already been achieved in the field of influencing particulate emission by aftertreatment of the exhaust gas. Methods for the after-burning of suspended soot and unburned high-boiling hydrocarbons as well as soot removal by exhaust gas filtration are especially prominent here.
The Forschungsgesellschaft fur Energietechnik und Verbrennungsmotoren mBH in Aachen West Germany has published a study by Dr. Herman Weltens entitled "Moglichkeiten zur Beeinflussung der Partikelemission von Dieselmotoren durch Abgasnachbehandlung (Possibilities for influencing the emission of particulates from diesel engines by aftertreatment of the exhaust gas"), on the occasion of a symposium in Esslingen West Germany on the 28th and 29th of Apr. 1980, which indicates the present state of the art.
On pages 15 and 16 of this publication in particular, attention is drawn to the fact that there is no certainty that the conditions required for spontaneous ignition and combustion of soot collected in the exhaust gas filter are reached sufficiently often in normal running conditions. It is thus proposed to oxidize the soot deposits intermittently with the aid of energy supplied from an external source. This external energy can be supplied by an open flame or by electric heating.
Without the aid of energy from an external source, the combustion of soot deposits on the surfaces of exhaust particulate filters is not possible with the methods known at the present time. This applies particularly to internal combustion engines which are supercharged by pressure wave machines. The only possibility here would be the insertion of exhaust particulate filters in the exhaust line downstream of the pressure wave machine.
However, small, low-pressure resistances are required in order to maintain low-pressure scavenging in the pressure wave machine at every operating point. When new, the pressure loss of an exhaust particulate filter is small and amounts to approximately 200 mm, water gage. The increase in the exhaust back pressure in the case of a blocked filter can in some circumstances lead to a breakdown of low pressure scavenging in the pressure wave machine and consequently to stalling of the engine.
Furthermore, the exhaust gas temperature downstream of the pressure wave machine is lower than, for instance, in the case of supercharging with a turbocharger, because of the proportion of scavenging air. The external energy supply for the combustion of the soot is greater when supercharging with a pressure wave machine.
One primary aim of the present invention is to remedy this problem. The present invention achieves the object of producing a device by which the particulate emission from internal combustion engines supercharged with pressure wave machines is limited to an optimum extent, by arranging an exhaust particulate filter in a high-pressure part of an exhaust gas system ahead of the pressure wave machine.
This arrangement of the exhaust particulate filter has the following advantages:
Saving of external energy;
Devices for the supply of external energy and soot combustion equipment for the combustion of soot deposits on the surfaces of the exhaust particulate filters by external energy are dispensed with;
Control equipment for initiating the ignition process of the external energy depending on the exhaust gas back pressure is also dispensed with;
The exhaust gas recirculation capability of the pressure wave machine itself is increased without the danger of fouling the rotor of the pressure wave machine;
After the ignition of the soot deposits the density of the charge air immediately increases again, the exhaust gas temperature decreases and the engine does not overheat;
Because the soot combustion reaction is exothermic, it continues undiminished in spite of a decreased exhaust gas temperature.
The filter is preferably arranged in the exhaust gas receiver itself. The advantage of this arrangement is apparent from the fact that the hot exhaust gases leaving the internal combustion engines can be utilized without losses for the combustion of the soot.
The filter is also preferably arranged in a segment separate from the exhaust gas receiver itself and immediately ahead of the pressure wave machine in the direction of exhaust gas flow and the filter is designed as an exchangeable constructional unit.
Thus the filter can be changed simply and rapidly.
The filter includes a monolithic, porous and heat-resistant core.
The particulates present in the exhaust gas impinge on the surface of the exhaust particulate filter and there agglomerate into larger particulates. The condition of the surface and the porosity of the material of construction of the exhaust particulate filter play a decisive role as regards the attachment and agglomeration processes of the soot particulates.
The core of the filter is surrounded by a fibrous, mat-like and heat-resistant covering.
The core of the filter together with the covering is arranged in a cylindrical carrier tube which is held at one end by the retaining ring provided in the exhaust gas receiver and at the other end by the retaining pin provided in the exhaust gas receiver.
Also, the cylindrical carrier tube is preferably secured between the flange of the exhaust gas receiver and the flange of the segment.
Thus, the core of the filter is rigidly held by the cylindrical carrier tube with intermediate positioning of the fibrous, mat-like covering and its position is accurately fixed in the axial and radial directions.
The carrier tube preferably includes a heat-resistant sheet metal. An elastic heat-resistant layer is arranged between the sheet metal and the solid jacket of the segment of the exhaust gas receiver.
In this way it is ensured that the carrier tube does not distort at relatively high temperatures, that it exhibits a high resistance to oxidation and that possible vibrations from the machine are damped by the elastic heat-resistant layer and thus not transmitted directly to the core of the filter.
The monolithic porous core of the filter preferably includes either a ceramic material with a high degree of stability with respect to temperature change or steel wool. With both these materials, optimum filter properties are achieved at relatively high temperatures when taking temperature variation into consideration.
In a method for operating the device, additional fuel is fed to the internal combustion engine in order to raise the exhaust gas temperature ahead of the particulates filter.
The charge air flap valve in the charge air line may be briefly closed in order to raise the exhaust gas temperature ahead of the filter and is then again operated normally after regeneration of the filter has taken place.
Alternatively, the recirculation flap valve in the fresh air suction line of the pressure wave machine may be briefly closed in order to raise the exhaust gas temperature ahead of the filter and may be operated normally again after regeneration of the filter has taken place.
Also alternatively, the exhaust gas temperature ahead of the filter may be raised by briefly opening the exhaust gas by-pass valve and then operating it again normally after regeneration of the filter has taken place.
The exhaust gas by-pass valve is arranged in the by-pass between the exhaust housing and the exhaust line of the pressure wave machine. The three operational steps outlined immediately above are alternatives. Thus a range of operating possibilities is available for raising the exhaust gas temperature ahead of the filter and burning off soot deposits on the surface of the filter.